1. Field of the Invention
The present invention relates to booster charge assemblies for borehole blasting and in particular to slider devices for coupling booster explosive charges to downline detonating cords.
2. Related Art
U.S. Pat. No. 4,938,143 issued Jul. 3, 1990 to R. D. Thomas et al and entitled "Booster Shaped For High-Efficiency Detonating", discloses a booster explosive having an "interface" surface at one end which is configured to contact a column of a relatively insensitive explosive while being directed towards the majority of the insensitive explosives content of the column. The body portion of the booster has sides which taper to an opposite, second end thereof which second end has a cross-sectional area which is smaller than the interface end. While Thomas et al discloses a wide variety of such tapered shapes and illustrates many in the drawings, the preferred embodiment is shown in FIG. 5 of Thomas et al wherein the booster explosive has generally the configuration of a frustrum of a right angle cone. The Thomas et al booster is disposed at or near the bottom of a borehole filled with a mass of insensitive explosive, typically a blasting agent, with the base facing upwardly towards the major portion of explosive within the borehole. Commercially available embodiments of the Thomas et al invention are known in which a booster explosive shaped generally similar to that illustrated in FIG. 5 of Thomas et al is encased within a molded synthetic polymeric (plastic) container. As illustrated in FIG. 5 of Thomas et al, the frusto-conical shaped booster contains three bores formed therein, one of which comprises a dead-end passageway (152) within which a blasting cap (154) is inserted, another of which passageway (148) extends through the booster explosive for passage therethrough of its signal transmitting cord (156) to the surface. A third passageway (146) extends along the longitudinal center axis of the booster explosive and is stated to permit threading therethrough of the signal transmission cord of another detonator positioned in the borehole below the illustrated booster.
A prior art cast booster device was sold under the trade designation DETADRIVE.TM.. The device comprised a polymeric ("plastic"), generally cylindrical container that defined a cylinder wall and a container bottom. The top of the container was open to facilitate pouring molten explosive therein. The bottom of the container was molded to define a detonator well and a central straw that defined a passage through the booster charge. The bottom of the container was configured to receive a coupling device that carried a percussion primer-activated detonator that was coupled to the detonating cord downline by an explosive coupling element. A similar coupling element and percussion primer-activated detonator are shown in U.S. Pat. No. 4,796,533 to Yunan, dated Jan. 10, 1989.